An antibody against cytochrome P-450b (induced by phenobarbital) did not significantly inhibit the O-dealkylation, N-dealkylation, and ring hydroxylation of oxprenolol by liver microsomes from untreated rats, or rats treated with phenobarbital or B-naphthoflavone. An antibody against cytochrome P-450c (induced by 3-methylcholantrene) did not inhibit the reactions by lever microsomes from untreated rats or phenobarbital treated rats but inhibited all three reactions by liver microsomes from rats treated with B-naphthoflavone, which also induces cytochrome P-450c synthesis.